Insulation has been utilized for decades to control the flow of tempered air. For example, insulation substantially prevents heat from flowing from a high temperature zone to a cool temperature zone. For example, the cool zone may be an interior of a structure such that the insulation helps maintain the cool internal temperature. Likewise, the interior temperature may be heated so that the insulation helps maintain the heated internal temperature. In other words, the insulation slows the rate of heat transfer.
Unfortunately, a change in either the inside or outside temperature is instantly reflected in the change in the rate of heat flow. Therefore, in order to maintain the desired internal temperature, the heating and cooling equipment must be able to respond quickly to changes in the temperature difference. Such is not always easy since the equipment must overcome a large volume of air or a large mass in the internal zone, both of which resist rapid temperature changes. Accordingly, during rapid external temperature fluctuations, the internal temperature is often either higher or lower than desired.
There lacks a method of maintaining a relatively constant rate of heat flow so as to maximize the efficiency of conventional heating and cooling equipment and to improve the correlation between the desired internal temperature and the actual internal temperature. Such a method would minimize the temperature variations and the energy output required to maintain a desired internal temperature.
Conventional forms of insulation comprise fiberglass rolls, batts, blankets and loose fill. Other types of insulation include cellulose, mineral wool and spray foam.
Materials known as phase change materials (“PCMs”) have also gained recognition as materials which alone, or in combination with traditional insulation, reduce home heating or cooling loads, thereby producing energy savings for consumer.
PCMs are solid at room temperature but as the temperature increases the PCMs liquefy and absorb and store heat, thus potentially cooling an internal portion of a structure. Conversely, when the temperature decreases, the PCMs solidify and emit heat, thus potentially warming the internal portion of the structure. Systems using PCMs with traditional insulation materials allow the PCMs to absorb higher exterior temperatures during the day and dissipate the heat to the internal portion of the structure at night when it tends to be cooler.
Known PCMs include perlite, paraffin compounds (linear crystalline alkyl hydrocarbons), sodium sulfate, fatty acids, salt hydrates and calcium chloride hexahydrate. While this list is not exhaustive, it is representative of the materials which exhibit properties common to PCMs.
In most current systems, both conventional insulation and PCMs are used in one or more known configurations. For example, U.S. Pat. No. 5,875,835 to Shramo and assigned to Phase Change Technologies, Inc., and incorporated herein by this reference, discloses packaged PCM placed between two layers of conventional insulation. U.S. patent application Ser. No. 11/061,199 to Brower and also assigned to Phase Change Technologies, Inc., and incorporated herein by this reference, discloses packaged PCMs used in combination with a single layer of conventional insulation. Regardless of the configuration, in high temperature environments, PCMs may remain liquefied for long periods of time such they are ineffective until such time that the ambient temperature drops below the PCM's transition temperature. Unfortunately, in warm climates, like desert locations in the Southwest United States, the temperatures may not drop below the PCM's transition temperatures for days or longer.
Consequently, there is a need for a controllable system and/or method that is able to return a liquefied PCM to its solid state in response to, for example, ambient temperatures exceeding the PCM's transition temperature. Such a controllable system and/or method is energy efficient and reduces or eliminates peak energy loads of those utilities providing the electricity or gas to a service area incorporating such systems and/or methods.